U.S. Pat. No. 7,431,467 (Title: “Portable Forensic Lighting Device”) discloses a cross-section converter for converting a circle-shaped light spot into an elongate rectangular light spot by means of mirrors. The elongate rectangular light spot is useful for detecting shoe prints at a crime scene. The disclosure of this patent document is hereby incorporated by reference.
The light source of the forensic lighting device described in U.S. Pat. No. 7,431,467 is an Hg-lamp having an extremely high pressure of Hg-vapor of about 200 atmospheres (2×107 Pa). The radiation of this lamp is spread over a spectral range from about 300 nm to 700 nm and is focused into a liquid light guide. The output radiation of the light guide is supplied to the cross-section converter which is a triangular shaped hollow body with metallized inner surfaces. The radiation undergoes multiple reflection in the interior of the reflector cavity and exits through a narrow elongate rectangular window made of acrylic glass. The intensity of the radiation is distributed rather homogeneously across the light output surface. The radiation spreads fan-shaped across the ground and facilitates the detection of weakly pronounced relief structures of shoe prints.